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Raspberry Pi Pico as AM Radio Transmitter

pesfandiar.com

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Re: Raspberry Pi Pico as AM Radio Transmitter

#11

Post by westurner »

bitwize wrote: post #3

This is the first use people cooked up for the MITS Altair computer, which at the time could only output to its blinkenlights without expansion. Before a tiny company called Micro-Soft released BASIC for the thing, some madlad at the Homebrew Computer Club found a way to spin the CPU in loops tight enough that the interference could be picked up as tones on an AM radio, allowing for music to be created. Good to see t…

GSMem (2015) 1-5.5m/30m with 3G from the RAM bus

TEMLEST-LoRa (2025) 87.5m with LoRa over display cables

LoPHY (2024) 700m with LoRA

MAGNETO (2021) CPU-generated magnetic fields

"Rowhammer for qubits" describes hypothetically using electron tunneling and magnetically biased bit flips in standard RAM to simulate quantum operators.

I've heard stories of ham radio clubs teaching how to make a coaxial antenna out of coaxial cable (cable TV copper cable)

"Can you hotwire this computer to transmit a tone through the radio?" — Transformers (2007)

Re: Raspberry Pi Pico as AM Radio Transmitter

#12

Post by crims0n »

mikeyouse wrote: post #9
hulitu wrote: post #2

> Raspberry Pi Pico as AM Radio Transmitter The fact that you are receiving it with an AM radio, doesn't mean that you are transmitting AM.

On off keying at 1,000khz is AM transmitting though?

AM is short for Amplitude Modulation, and by definition needs a carrier wave. This is more like controlled interference, still impressive though.

Re: Raspberry Pi Pico as AM Radio Transmitter

#13

Post by pesfandiar »

mk_stjames wrote: post #10

I want to point out that what keeps this 'OK' is that the little wire is so 'electrically short' compared to the actual wavelength at 1000khz (a real quarter wave antenna at that freq is like 75 meters)... and thus this limits the power of this 'transmitter' to probably nanowatts. If the PIO pin could drive a fair amount of current at 3.3v into a long enough wire at that frequency you'd start to get into milliwatts,…

Mea culpa.

Without the proper knowledge or measurement equipment, I observed that the audio would fade out after a 30 cm distance. Combined with running it for mere seconds to test and record a demo, I assumed to be in the clear with the spirit of the regulations. Appreciate the reminder to be responsible with RF.

Re: Raspberry Pi Pico as AM Radio Transmitter

#14

Post by anfractuosity »

pesfandiar wrote: post #6
nom wrote: post #5

Earlier quoted context omitted.

https://vanhunteradams.com/Pico/AM_Radio/AM.html

Highly recommend his Pico-based microcontroller course: https://www.youtube.com/playlist?list=PLDqMkB5cbBA4GisLzRSqw... The PWM-based modulation is interesting, but as an amateur, I couldn't fully understand it or trust that the radio receiver reliably picks up the duty cycle as amplitude.

If you PWM a signal, I presume you could add a filter to convert to amplitude changes?

Re: Raspberry Pi Pico as AM Radio Transmitter

#16

Post by mschuster91 »

westurner wrote: post #11
bitwize wrote: post #3

This is the first use people cooked up for the MITS Altair computer, which at the time could only output to its blinkenlights without expansion. Before a tiny company called Micro-Soft released BASIC for the thing, some madlad at the Homebrew Computer Club found a way to spin the CPU in loops tight enough that the interference could be picked up as tones on an AM radio, allowing for music to be created. Good to see t…

GSMem (2015) 1-5.5m/30m with 3G from the RAM bus TEMLEST-LoRa (2025) 87.5m with LoRa over display cables LoPHY (2024) 700m with LoRA MAGNETO (2021) CPU-generated magnetic fields "Rowhammer for qubits" describes hypothetically using electron tunneling and magnetically biased bit flips in standard RAM to simulate quantum operators. I've heard stories of ham radio clubs teaching how to make a coaxial antenna out of coax…

> GSMem (2015) 1-5.5m/30m with 3G from the RAM bus

What the fuck, that's crazy. For those similarly bewildered, look here [1].

[1] https://www.usenix.org/conference/usenixsecurity15/technical...

Re: Raspberry Pi Pico as AM Radio Transmitter

#17

Post by anfractuosity »

westurner wrote: post #11
bitwize wrote: post #3

This is the first use people cooked up for the MITS Altair computer, which at the time could only output to its blinkenlights without expansion. Before a tiny company called Micro-Soft released BASIC for the thing, some madlad at the Homebrew Computer Club found a way to spin the CPU in loops tight enough that the interference could be picked up as tones on an AM radio, allowing for music to be created. Good to see t…

GSMem (2015) 1-5.5m/30m with 3G from the RAM bus TEMLEST-LoRa (2025) 87.5m with LoRa over display cables LoPHY (2024) 700m with LoRA MAGNETO (2021) CPU-generated magnetic fields "Rowhammer for qubits" describes hypothetically using electron tunneling and magnetically biased bit flips in standard RAM to simulate quantum operators. I've heard stories of ham radio clubs teaching how to make a coaxial antenna out of coax…

Based on a repo I found that twiddled the memory bus, I transmitted audio from a wav file via Pulse Density Modulation - https://github.com/anfractuosity/musicplayer

Re: Raspberry Pi Pico as AM Radio Transmitter

#19

Post by alnwlsn »

mk_stjames wrote: post #10

I want to point out that what keeps this 'OK' is that the little wire is so 'electrically short' compared to the actual wavelength at 1000khz (a real quarter wave antenna at that freq is like 75 meters)... and thus this limits the power of this 'transmitter' to probably nanowatts. If the PIO pin could drive a fair amount of current at 3.3v into a long enough wire at that frequency you'd start to get into milliwatts,…

At least you are supposed to be allowed to transmit on AM (and FM) bands at very low power, at least under FCC rules. That's how they can sell those adapters for car radios. Some other ones you definitely are not supposed to use as far as I know, like the old analog TV signals - I've seen a couple of those sorts of projects recently. On the other hand, you can go and buy an illegal TV transmitter on Amazon right now.

Also a reasonably even bet that you already own a low-quality wall power supply that will produce more interference than anything you're going to be doing with a Pico and a 4" jumper wire (I've found a couple of offending devices in my house), but I'm certainly in no position to tell you if you should or shouldn't do something.

Re: Raspberry Pi Pico as AM Radio Transmitter

#20

Post by cadr »

pesfandiar wrote: post #13
mk_stjames wrote: post #10

I want to point out that what keeps this 'OK' is that the little wire is so 'electrically short' compared to the actual wavelength at 1000khz (a real quarter wave antenna at that freq is like 75 meters)... and thus this limits the power of this 'transmitter' to probably nanowatts. If the PIO pin could drive a fair amount of current at 3.3v into a long enough wire at that frequency you'd start to get into milliwatts,…

Mea culpa. Without the proper knowledge or measurement equipment, I observed that the audio would fade out after a 30 cm distance. Combined with running it for mere seconds to test and record a demo, I assumed to be in the clear with the spirit of the regulations. Appreciate the reminder to be responsible with RF.

I don’t know what the regulations are in your country (looks like you are maybe in Canada?), but in many countries it is straightforward to get an amateur radio license, and then you can have all sorts of fun (under the rules).
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